Pressure transducers have been widely employed in many environments in order to monitor pressure. Such environments include very harsh environments such as monitoring pressure in automotive internal combustion engines, aircraft engines as well as in other environments which are subjected to relatively high pressures and high temperatures. It is desirable to monitor engine pressures in order to determine proper operation of an engine during extreme conditions. These engines can of course be automotive engines, or aircraft engines as well as engines utilized in missiles or in other devices.
A purpose of taking pressure measurements in conjunction with engines is to determine the fuel and oil filter pressures and thus, to provide pressure data that will be used to determine important engine filter maintenance. As one can ascertain, especially in regard to aircraft engines, the measurement of pressure regarding the engine fuel filter and oil filter pressures involve relatively high temperatures as well as high pressures.
Pressure is determined in terms of an absolute pressure, so that the absolute pressure can be monitored to determine overall engine performance and also to determine when the filters need to be replaced. This can be done by utilizing the pressure measurements obtained from the pressure transducer and applying such measurements to a microprocessor or other computing device to determine when pressures fall outside a desired range and therefore to make some determination of whether the filters have to be replaced.
In order to facilitate such measurements, it would be desirable to reduce the number of pressure transducer assemblies required to determine such operation. Cognizant of this problem, the prior art would utilize two independent absolute measurements for each filter. One pressure transducer would be upstream of the filter and one pressure transducer would be downstream of the filter. In this manner there would be four transducers utilized per engine. In order to reduce the number of transducers, the present approach enables one to mount two independent sensors into two different transducers. In this manner the fuel filter transducer would measure pressure both upstream and downstream and the oil filter transducer would perform the same function.
The apparatus according to embodiments of the present invention would allow two less transducers per engine and result in a reduced interface piece per count at a reduced weight and lower cost.
Use of two pressure sensors in one transducer is described in, for example, U.S. Pat. No. 6,272,928 entitled “Hermetically Sealed Absolute and Differential Pressure Transducer” issued on Aug. 14, 2001 to A. D. Kurtz, and assigned to the assignee herein Kulite Semiconductor Products, Inc. That patent depicts a single semiconductor chip which includes dielectrically isolated leadless pressure sensors adapted to simultaneously measure a first pressure and a differential pressure between the first pressure and a second pressure. The chip includes a wafer, which includes first and second recessed portions defining first and second diaphragm areas. There is a rim portion formed between the first and second recess portions for isolating the first diaphragm from the second diaphragm. A first circuit is mounted on the first diaphragm and responsive to the first pressure and a second circuit is mounted on the second diaphragm and responsive to the second pressure. The first and second circuits can be electrically coupled to one another so as to cooperatively provide a common output indicative of differential pressure associated with the first and second pressures, while simultaneously providing an output indicative of either the first or second pressures.
FIG. 1 of the above-noted patent illustrates a plan view of a sensor structure formed on a single wafer. The structure includes two independent open four active arm Wheatstone bridges each having six contact areas or fingers respectively. Each bridge has its own active area defined by an associated deflectable diaphragm. Open bridges are depicted in FIG. 2 of the patent and the various bridge configurations can be interconnected to provide an output proportional to the pressure difference between a first and second pressure as well as providing an output indicative of the first and second pressures. Also indicated in that patent are other instances where it is necessary to simultaneously measure both the absolute and differential pressure. Such devices can be used to determine aircraft speed where speed is measured by measuring the total pressure which is the pressure against the nose of the aircraft as it moves through the air and the static pressure which is the atmospheric pressure surrounding the aircraft. The air speed is proportional to the difference between a total and static pressure. See also U.S. Pat. No. 6,612,179 issued on Sep. 2, 2003, entitled “Method and Apparatus for the Determination of Absolute Pressure and Differential Pressure Therefrom” to A. D. Kurtz, and assigned to Kulite Semiconductor Products, Inc. That patent depicts a combination absolute and differential pressure sensing device, which includes a plurality of absolute pressure transducers, each transducer including a plurality of half-bridge piezoresistive structures. The device selectively couples at least one of the plurality of half-bridge structures through a first one of the absolute pressure transducers to form a half active full bridge structure adapted to measure an absolute pressure. At least one other of the plurality of half bridge piezoresistive structures is connected to at least one of the half bridge structures of a second absolute pressure transducer to form a full bridge adapted to measure a differential pressure. The structure is depicted in FIG. 1 and FIG. 2 of the above patent, with various circuit configurations depicted in FIGS. 3-6. See also U.S. Pat. No. 7,057,247 entitled “Combined Absolute Differential Transducer” issued on Jun. 6, 2006 to A. D. Kurtz et al and assigned to the assignee herein. That patent describes a combined absolute differential pressure transducer which consists of two sensors made from the same silicon wafer. The patent shows both separate absolute and differential sensor wafers or dies as well as a single wafer or die containing only an absolute and differential pressure sensor.
Although prior patents illustrate providing two pressure sensors in a single pressure transducer structure, it is however, desirable to provide an improved pressure transducer assembly for monitoring engine parameters such as fuel and oil filter pressure values in an engine, in a simplified and economical manner and with high temperature operation, in a relatively small and rugged device.